Radio frequency communication devices, such as two-way radios or cellular telephones, are known to have circuitry to receive or transmit radio frequency signals via an antenna. The antenna is the critical element of a radio frequency communication device and antenna performance and radiation efficiency is often considered as an important attribute of such devices. A monopole antenna that extends from a housing of the radio frequency communication device is often used to obtain both good antenna performance and radiation efficiency.
One part of a monopole antenna assembly that affects the antenna performance is the counterpoise. Theoretically, a counterpoise provides a radiation pattern that is opposite that of the radiation pattern provided by the monopole antenna. Accordingly, one end of the monopole antenna is coupled to and extends away from a feed point and the counterpoise is also coupled to and extends away from the feed point in an opposite direction from the monopole antenna. The surface area (size) and positioning of the counterpoise are important antenna design considerations and historically the counterpoise for a two-way radio or cellular telephone was formed primarily by metallic conductors on their main circuit board.
In recent years there is a desire for smaller hand held communication devices and accessories that require antennas. One such accessory is a Public Safety Microphone that when in use is operatively coupled by a cable to a two-way radio typically mounted on a belt of a user. Typically, these smaller hand held communication devices and accessories inherently have a relatively small main circuit board and thus the surface area for a counterpoise that can be provided by the circuit board may be insufficient for providing good quality antenna performance.
In order to overcome the insufficient circuit board counterpoise surface area associated with relatively small main circuit boards, the counterpoise can be provided by a conductive paint coating or conductive ink coating that is sprayed onto the inside surface of a device's housing. Typically, this housing comprises two opposing housing members and the inside surface of both members has the coating sprayed or otherwise deposited thereon. Hence, the main circuit board is surrounded by the counterpoise and thus the radiation pattern of the antenna is not substantially attenuated or distorted by the components of the device.
Although conductive coatings on the inside surface of the housing provides a basis for good antenna performance, such coatings are relatively expensive due to both the cost of the paint and the cost associated with depositing the coating on the inside surfaces.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.